In the past, the semiconductor industry used different device structures and methods to form insulated gate field effect transistor (IGFET) devices. One particular structure for vertical power IGFET devices used trenches that were formed in an active area of the device. A portion of those trenches were configured as the gate regions of the device. Some of these transistors also had a shield conductor or field plate that was tied to source and configured to assist in improving blocking voltage performance and lowering the gate-to-drain capacitance of the device.
In order for the field plate to favorably impact device performance, very tight geometries are required. Past methods for forming IGFET devices with trench field plates relied on a complex series of process steps, and used thick oxidation layers overlying the trench gate regions to form self-aligned source and body contacts. These thick oxidation layers prevented the use of gate silicide structures, and required the use of thicker epitaxial layers, deeper trenches, and deeper etched contacts. All of these factors reduced the overall manufacturability of the device.
Accordingly, it is desirable to have a scaleable, self-aligned process for forming the device structure, which results in better device performance, reliability, and lower costs.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position or state. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described. For clarity of the drawings, doped regions of device structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions generally may not be straight lines and the corners may not be precise angles.
In addition, although the source is normally shown on the top or upper surface of the device and the drain is normally shown on the bottom or lower surface of the device, such orientation is reversible. Additionally, the drain and source contacts may be on the same or opposite surfaces.
Moreover, the description may illustrate a cellular design (where the body regions are a plurality of cellular regions) or a single body design (where the body region is comprised of a single region formed in an elongated pattern, typically in a serpentine pattern or formed in a plurality of stripes). However, it is intended that the description is applicable to both a cellular implementation and a single base implementation.